gravitational wave detector Yuta Michimura Department of Physics, - PowerPoint PPT Presentation

Ando Lab Seminar November 28, 2019 Science with even smaller scale space gravitational wave detector Yuta Michimura Department of Physics, University of Tokyo

Contents • Introduction - Deci-hertz GW astronomy - How to proceed with DECIGO • Recap of F-DECIGO plan (60 km, 2 kg) - Concept - Science cases (including dark matter) • FF-DECIGO plan (100 m, 100 g) - Background - Concept - Science cases (especially stochastic background) - Possibility of longer arms • Summary 2

Deci-hertz GW Astronomy • Even more interest after the dawn of GW astronomy - Intermediate-mass BH - IMRIs - White dwarf binary and Type Ia SNe - Stochastic background - Dark matter search (Ultralight boson from BH superradiance) 3 arXiv:1908.11375

Detectors We Usually Discuss LISA: https://perf-lisa.in2p3.fr/ KAGRA: PRD 97, 122003 (2018) TianQin: arXiv:1902.04423 (from Yi-Ming Hu) aLIGO: LIGO-T1800044 B-DECIGO: PTEP 2016, 093E01 (2016) ET: http://www.et-gw.eu/index.php/etdsdocument CE: CQG 34, 044001 (2017) TianQin LISA KAGRA B-DECIGO aLIGO Einstein Telescope Cosmic Explorer 4

Other Proposals • There are so many proposals in deci-hertz band (this is not a complete list at all!) 5

Zoo of Proposals • DECIGO CQG 28, 094011 (2011) • ALIA arXiv:1907.11305 (post LISA, 500,000 km) • BBO CQG 23 4887 (2006) (post LISA, 50,000 km) • TOBA PRL 105, 161101 (2010) (10m torsion bar) • GEOGRAWI arXiv:1111.2576 (73,000 km LISA) -> gLISA arXiv:1608.04790 • GADFLI arXiv:1111.3708 (73,000 km LISA) • LAGRANGE arXiv:1111.5264 (660,000 km LISA) • OMEGA white paper (2011) (1,000,000 km LISA) • SAGE arXiv:1811.04743 (Sagnac interferometer) • AMIGO arXiv:1709.05659 • MAGIS arXiv:1711.02225 (atom interferometer) • Taiji arXiv:1807.09495 (almost LISA) • INO arXiv:1809.10317 (optical lattice clocks) • SAGE arXiv:1907.03867 (atom interferometer or atomic clocks) • TianGO arXiv:1908.06004 (100 km, 10 kg Michelson with squeezing) • DO arXiv:1908.11375 (1e8 m LISA, Voyage2050) • SOGRO IJMPD 28, 1940001 (2019) (superconducting) 6

Comparison of Proposals • Wei-Tou Ni, IJMPD 25, 1630001 (2016) • Almost every proposal is LISA-type 7

How to Proceed with DECIGO? • There’s a high possibility that DECIGO require international collaboration • But almost all the other proposals are LISA-type • Fabry-Pérot type pathfinder is necessary to show the feasibility, and we might be the only ones who think it is necessary • We want to do it quick and yet we want to do some science → Small-scale mission ( 公募型小型 ) Launch with Epsilon rocket 150 億円 8

Meeting on Nov 21, 2019 @ JAXA • Akutsu-san, Izumi-san, Ito-san, Shoda-san, me • Meeting to define DECIGO mission 9

やばいものリスト • Fabrication and handling of large mirror • Telescope - Inside or outside of the cavity ? - Adaptive optics ? • Inertial sensor and thruster • Length sensing and control vs orbit • Link acquisition • Force / acceleration noise requirement 10

やばいものリスト • Fabrication and handling of large mirror • Telescope - Inside or outside of the cavity ? - Adaptive optics ? • Inertial sensor and thruster • Length sensing and control vs orbit • Link acquisition • Force / acceleration noise requirement → Some part can be demonstrated with small-scale mission 11

Recap of F-DECIGO Concept • Minimum success: Formation flight demonstration • Full success: End-to-end demonstration of the sensitivity Force noise evaluation • Extra success: Multi-wavelength GW observation Intermediate mass BH search • Use already-demonstrated parameters 12

F-DECIGO Designed Sensitivity • 60 km, 2 kg, finesse 10, 10 mW, 4e-15 N/rtHz TianQin LISA B-DECIGO 13

F-DECIGO Horizon Distance B-DECIGO LISA ET TianQin CE z=10 aLIGO z=1 F-DECIGO IMBH search KAGRA upto z~1 GW150914 O1 and O2 GW170817 binaries plotted 14 Optimal direction and polarization SNR threshold 8

F-DECIGO Science Cases • First real IMBH search 48 event/year (SNR>8, optimistic) H. Shinkai+, ApJ 835, 276 (2017) • Estimate merger time and location of BNS For 1.4 Msun-1.4 Msun @ 40 Mpc, ~100 sec and 10 3 deg 2 precision is possible But SNR is around 2 H. Takeda+, PRD 98, 022008 (2018) week day hour ISCO week day hour ISCO Observation from a month before the merger Median over the angles 15 week day hour ISCO

Dark Matter Search also Possible • Axion search with polarization measurement K. Nagano, T. Fujita, YM, I. Obata, PRL 123, 111301 (2019) • Vector DM which couples to B-L charge A. Pierce+, PRL 121, 061102 (2018) • Sensitivity not very good F-DECIGO CAST SN1987A aLIGO F-DECIGO DECIGO Cosmic Explorer Equivalence aLIGO principle tests LISA DECIGO 16

Technical Feasibility • 4e-15 N/ √ Hz force noise (Residual gas of 1e-6 Pa) Demonstrated by LISA Pathfinder DECIGO requirement is PRL 120, 061101 (2018) 1e-16 N/ √ Hz • 2 kg mirror and housing, vacuum tank Similar to LISA Pathfinder • 60 km arm length GFO proof mass is 72 g GRACE-FO demonstrated 200 km Link acquisition is also demonstrated PRL 123, 031101 (2019) 17

History of Iterations • April 2019 : C-DECIGO (10 km, 10 kg) proposal at Ando Group Midterm Seminar (slide) • May 2019 : C-DECIGO (10 km, 10 kg) proposal at FF meetup (slide) -> downgraded to F-DECIGO (10 km, 2 kg) to reduce mass • Sep 2019 : Refined F-DECIGO plan (60 km, 2 kg) assuming LPF-level force noise and focusing on applying to 公募型小 型 at JPS meeting (slide) • Nov 2019 : 60 km, 2 kg plan presented at DECIGO workshop (slide), Letter of Intent to 公募型小型 -> 100 m and 100 g plan (Let’s call it FF-DECIGO) was proposed from the limitation of Epsilon rocket and actuation dynamic range 18

Why 100 m and 100 g • 180 kg / satellite @ 800 km altitude would be realistic to launch with Epsilon (previously we are thinking of 350 kg / satellite @ 1800 km) • 25 kg package with 72 g proof mass was used for GRACE-FO and probably similar for small-scale mission • Relative acceleration from J2 term being too much in geocentric orbit Earth gravity constant J2 coefficient Arm length Earth radius Orbital altitude 19

Relative Force from J2 Term • Relative force from J2 is constant if m*L=const. • m*L = 100 g * 100 m gives 4e-8 N from J2 • Force noise requirement 4e-15 N/rtHz • Dynamic range 10 7 should be within our reach (~10 9 with good analog circuits) 60 km * 2 kg detector at 1800 km → 2e-4 N from J2 1800 km 100 m * 100 g detector at 800 km 800 km → 4e-8 N from J2 6400 km Calculation done with T. Ito’s code 20

J2 Term and Sensitivity • If orbital altitude and dynamic range is given, achievable strain sensitivity can be calculated dynamic range with altitude 800 km and dynamic range 10 7 • You cannot win by increasing m or L !!! 21

FF-DECIGO Concept • Focus on the demonstration of formation flying and the demonstration of the end-to-end demonstration as a gravitational wave detector • By (kind of) giving up GW detection 22

FF-DECIGO Finesse • Finesse can be higher than F-DECIGO, upto radiation pressure noise being ~4e-15 N/rtHz F-DECIGO B-DECIGO Shot noise 5e-22/rtHz 1e-21/rtHz Assumed mirror g-factor = 0.3 diameter/thickness = 5 wavelength 515 nm FF-DECIGO 23

FF-DECIGO Designed Sensitivity • 100 m, 100 g, finesse 1000, 10 mW, 4e-15 N/rtHz TOBA TianQin FF-DECIGO LISA B-DECIGO 24

FF-DECIGO Horizon Distance B-DECIGO LISA ET CE TianQin z=10 F-DECIGO aLIGO z=1 KAGRA TOBA GW150914 FF-DECIGO GW170817 25

FF-DECIGO Science Case • IMBH probably O(10 -8 ) event / year • Dark matter search worse than F-DECIGO • Upper limit to stochastic GW background FF-DECIGO 26 Data from Y. Kuwahara

Comparison with Other Proposals • Worth a try if we can do faster than LISA, TianQin and 3G (and SOGRO etc.) TianQin FF-DECIGO LISA B-DECIGO 27

Comparison with Prototypes • Improvement by many orders of magnitude Data from T. Shimoda Phase 1 Prototype TOBAs Cryo Phase 2 LISA Pathfinder 1.96 kg, 38 cm Phase 2.5 Phase 3 TOBA TorPeDO prototype 28

Possibility of Longer Arms • Sensitivity and horizon distance scales linearly with arm length if intra-cavity power is constant and J2 term is somehow OK • Can be longer F-DECIGO B-DECIGO upto ~2 km from diffraction Shot noise loss 5e-22/rtHz 1e-21/rtHz FF-DECIGO 29

Mode-Match Degradation • Assume mode-match is designed for 100 m and arm length is changed in orbit • Sensitivity scales almost linearly upto ~1 km with larger g-factor Only mode mismatch Including diffraction loss Compensation could be possible with adaptive optics and mode match tuning 30

Summary • F-DECIGO (60 km, 2 kg) might not be possible but FF-DECIGO (100 m, 100 g) could be possible with Epsilon-class mission • Considering J2 term, if altitude and dynamic range is fixed, achievable strain sensitivity can be calculated and you cannot win by increasing the mirror mass or arm length • Almost no chance of FF-DECIGO detect gravitational waves, but still it can search for stochastic GW background with unpreceded sensitivity at ~1 Hz • Changing the arm length in orbit sounds feasible 31